Among the conventionally-known riding lawn mowers is the so-called rotary lawn mower which cuts grass by rotating a cutting blade, accommodated in a downwardly-opening housing, along the surface of grass. Examples of such a rotary lawn mower include a type for use in a mulching mode and a type for use in a bagging mode. The lawn mower for use in the bagging mode collects grass cut by the cutting blade (i.e., cut grass or grass clippings) in a grass clippings receptacle, while the lawn mower for use in the mulching mode chops the grass clippings into finer pieces within the housing and discharges the thus-chopped glass clippings downward of the housing.
However, it is often inconvenient to use such two types of lawn mowers depending on intended purposes. So, recent years have seen development of a technique for allowing a single riding lawn mower to be used in both of the bagging and mulching modes. More specifically, such a riding lawn mower operable in both of the bagging and mulching modes is manually switchable between the bagging mode in which a shutter plate is placed in a fully opened position to allow grass clippings to be collected in the grass clippings receptacle and the mulching mode in which the shutter plate is placed in a fully closed position to allow glass clippings to be discharged downward of the housing.
A similar technique to the aforementioned is known from Japanese Patent Application Laid-Open Publication No. SHO-63-063306 (hereinafter referred to as “Patent Literature 1”), Japanese Patent Application Laid-open Publication No. 2000-050716 (hereinafter referred to as “Patent Literature 2”) and Japanese Patent No. 3418136. More specifically, from Patent Literatures 1 to 3, a riding lawn mower is known, in which a path for delivering grass clippings from the housing to the grass clippings receptacle is controlled via a shutter mechanism so as to discharge the grass clippings onto the ground surface.
The riding lawn mower known from Patent Literatures 1 to 3 includes the shutter mechanism provided on a grass clippings delivery passage over which grass cut by the cutting blade (i.e., grass clippings) is delivered from the housing to the grass clippings receptacle. The shutter mechanism includes a horizontal pivot shaft (hinge shaft) disposed on a lower portion of the grass clippings delivery passage, and the shutter plate pivotable about the pivot shaft for opening and closing the grass clippings delivery passage. More specifically, the shutter plate is pivotable between a fully closed position where it closes the grass clippings delivery passage and a fully opened position where it is laid down toward an entrance of the grass clippings delivery passage for opening the grass clippings delivery passage. Namely, the shutter mechanism employed in the riding lawn mower disclosed in Patent Literatures 1 to 3 is of a rear hinge type where the pivot point of the shutter plate is located at a rear portion of the shutter plate. In the so-called rear-hinge-type shutter mechanism, the shutter plate in the fully opened position is laid down in a direction opposite from a direction where grass clippings and delivering air flow from the housing to the grass clippings receptacle.
The delivering air for delivering grass clippings from the housing to the grass clippings receptacle flows along the grass clippings delivery passage. Such grass clippings delivering air differs in velocity or force (i.e., kinetic energy of the delivering air) between when the lawn mower is in the middle of a grass cutting operation and when the lawn mower is starting or stopping the grass cutting operation. More specifically, the force of the grass clippings delivering air when the lawn mower is starting or stopping the grass cutting operation is smaller than that when the lawn mower is in the middle of the grass cutting operation. When the force of the grass clippings delivering air is small, the grass clippings would fall onto the bottom surface of the grass clippings delivery passage halfway through the delivery. Particularly, a lot of heavy grass clippings (e.g., grass clippings containing much moisture content) would accumulate on the bottom surface of the grass clippings delivery passage. Generally, the shutter mechanism has a stepped section on or near the hinge section, and grass clippings would easily accumulate on the stepped section.
In the rear-hinge-type shutter mechanism, dispensing with the stepped section is one conceivable approach to avoid the aforementioned problem. Such an approach, however, is not advisable in that not only the shutter mechanism would become complicated in construction but also there would arise a need to greatly change the shape of the grass clippings delivery passage. Generally, because grass clippings delivering air of a relatively great pressure is generated when the operation of the lawn mower has been started again, it has been conventional to use such grass clippings delivering air of a relatively great pressure to blow away, to some extent, the grass clippings accumulated on the bottom surface of the grass clippings delivery passage.
However, in the rear-hinge-type shutter mechanism, the grass clippings delivering air flowing along the delivery passage would decrease in force at and around the hinge section. Thus, grass clippings falling on the bottom surface of the delivery passage would still accumulate on the stepped section formed on the hinge section. Besides, it is difficult for the grass clippings delivering air to reach a neighborhood behind the hinge section. Substances deposited on the neighborhood behind the hinge section may often remain deposited because the blowing-away force of the grass clippings delivering air applied to that neighborhood is weak. Besides, it is preferable to minimize the frequency of maintenance/inspection and cleaning operations to be performed on the shutter mechanism.